U.S. Department of Defense


Date of this Version



NAVIGATION: Journal of The Institute of Navigation Vol. 0, No. 0, 2017, Printed in the U.S.A.


U.S. government work.


The next generation Global Positioning System (GPS) ground control segment will entail a number of GPS ground system upgrades from the existing ground control segment. One of these upgrades is the inclusion of a new modernized timescale algorithm used to generate GPS Time. The timescale is currently being designed as a separate modular unit (given the acronym ETF, or Ensemble Timescale Filter) within the ground system navigation package and is based upon a U-D Kalman Filter implementation that utilizes measurements of all clocks in the ground network and satellite constellation.

The new ETF module will include a number of features that improve the stability of the GPS Time timescale and provide more user/operator autonomy to include: multi-weight clock weighting for better handling of mixed clock types in the same filter; automated clock break detection and handling; robust outlier and anomalous clock behavior mitigation; admission of multiple external timescale solutions, including alternate ETF realizations; and adaptive clock parameter estimation. The preliminary results presented in this paper demonstrate some of the performance capabilities and robustness characteristics of the ETF.